MIPS has 32 x 32-bit registers

• 0 ~ 31

• 32-bit data is called a ”word”

  • exact definition of word: the natural unit of access in a computer, usually a group of 32 bits; corresponds to the size of a register in the MIPS architecture.

• Why only 32 registers?

the MIPS convention is to use two-character names following a dollar sign to represent a register:

Assembler names

• $t0,$t1,…,$t9 for temporary values
• $s0,$s1,…,$s7 for saved variables

for example, if we want to calculate f = (g + h) - (i + j); in c, we don’t need to save intermediate values (g + h), (i + j) . Thus we can write as:

add $t0, $s0, $s1
add $t1, $s2, $s3
sub $s4, $t0, $t1

where $s0, $s1, $s2, $s3 each corresponds to g, h, i, j .

Arithmetic Operation only occur on registers in MIPS instructions. Therefore there needs to be data transfer instructions.